Machine assisted interpersonal communication has simplified both business and personal communications, and has enabled the source and receiver of a communication to be separated in both time and space. Devices for machine assisted interpersonal communication range from the simple answering machine to smartphone-based translation systems that can interpret a language (e.g., French) and translate it into another language for the smartphone user (e.g., spoken or written English).
One specific application of machine assisted interpersonal communication is sign language translation. A sign language (also known as signed language) is a language that uses manual communication to convey meaning, ideas and thoughts, which simultaneously employs hand gestures, movement, orientation of the fingers, arms or body, and facial expressions to convey a speaker's ideas. The complexity of sign language may be captured, in part, by using multiple input and output modalities for its translation and communication.